EFFECT OF LEAD ON THE DEVELOPMENT OF AUDITORY TEMPORAL PROCESSING

University Of Montana, Missoula MT

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Abstract

Lead remains an important environmental toxicant despite it's removal from paint and gasoline in the United States and lead exposure (especially in children) remains a significant problem. The CDC reports that 930,000 U.S. children have blood-lead concentrations greater than 10 pg/dL (beyond a safe concentration). In states like Montana, where mining has resulted in regionally high levels of lead in the environment, there are focal regions where lead levels in children are significantly higher than the national average. Early exposure to lead is known to be a risk factor for reading disability (RD). While there are many reports linking lead exposure to reading disabilities, it is not clear how lead is able to exert its effects on language and perception. Significantly, recent preliminary studies conducted by our collaborator Dr. Lincoln Gray (UT-Houston) indicate that lead-exposed children and animals show deficits in backward masking. Backward masking is the ability to hear a short tone pip that occurs immediately before a louder and longer masking noise This suggests a link between lead exposure, auditory processing deficits, and dyslexia because children with dyslexia are deficient in backward masking. These deficits in auditory perception are not the result of general hearing loss and the deficit in basic auditory processing that accompanies dyslexia appears to be specific for temporal auditory processing (how auditory information is processed over very short periods of time). We have discovered that chickens exposed to low levels of lead (<10 Fg/dL) during development not only show deficits in backward masking, but also exhibit significant anatomical changes of neurons and glial cells within the auditory brainstem. We hypothesize that low levels of lead induce neuroanatomical changes within the auditory brainstem that then result in deficits in backward masking. This proposal will determine whether low levels of lead 1) reliably induce deficits in backward masking in lead-exposed children and 2) result in neuroanatomical, changes within the mammalian auditory system that could be the anatomical correlate for these behavioral deficits. The proposed studies will link auditory behavioral data with anatomical changes in order to elucidate whether low levels of lead produce changes within the mammalian auditory system. If so, the definition of a minimal toxic lead level in children will need to be reduced below the 10 p.g/dLstandard currently in use.